This invention relates generally to threaded fasteners. It relates particularly to locking fasteners of the type employing a threaded nut and a locking washer.
A locking fastener or locking fastener assembly is employed to prevent loosening of a threaded fastener element in a fastener joint. There are numerous types of joints in which locking fasteners or fastener assemblies are not only desirable but necessary to prevent a nut from loosening. One such application is in the axle and wheel nut assembly of a motor vehicle or the like.
In a typical axle and wheel nut assembly, the hub is supported on a spindle by axle bearings which permit the hub, and thus a vehicle wheel, to rotate on the spindle. An axle bearing nut is threaded onto the free end of the spindle and holds the axle bearings and bearing races together in a predetermined relationship. The axle bearing nut must be set in precisely the proper position on the spindle to apply end loading on the bearing races sufficient to avoid excessive play in the bearings but insufficient to overload them, the result of either being possible bearing failure or even loss of a wheel.
Numerous types of nuts with positive locking components are well known. One of the oldest and most common of these is the conventional castellated nut and cotter pin assembly. The disadvantages of these assemblies are numerous. They include the necessity of carefully locating a hole through the axle spindle, of using an extra component, of reduced nut strength, of relatively long installation time and of the difficulties encountered in fine tuning the preload on the bearing races.
Newer developments in locking fastener assemblies include those found in the Anderson, Jr. U.S. Pat. No. 3,762,455, the Grube U.S. Pat. No. 4,812,094, the Burdick U.S. Pat. No. 5,533,849, and the Peterkort U.S. Pat. No. 5,597,278, for example. Of these, the Grube and Peterkort patents are assigned to the same assignee as the present invention, as will be noted.
The Peterkort patent discloses a locking fastener assembly consisting of a flanged nut and a retainer washer loosely seated on the nut""s flange. The retainer washer includes a radially inwardly extending tab which is designed to slide axially along a slot in a threaded spindle while preventing the washer from rotating relative to the spindle. A releasable locking clip is positioned to lock the nut to the washer. The locking clip is released by engagement of a wrench socket with a hex-head on the nut so that the nut can be threaded to a desired bearing loading position. When the wrench is removed, the clip interlocks the washer and nut to prevent the nut from rotating.
The aforedescribed Peterkort locking fastener assembly is a highly effective device for use in vehicle wheel assemblies. It is simple and relatively inexpensive. However, its design focuses on limiting end play, not maintaining a constant preload.
Other known locking fastener designs include prevailing-torque locking fasteners. Locking action is achieved with frictional resistance induced between mating threads. There is positive resistance to assembly, which maintains throughout fastener seating and tightening. A high residual resistance to loosening remains even if fastener preload is lost. Disassembly is even difficult. Complete disengagement in service is highly unlikely. Prevailing-torque fasteners are generally all-metal fasteners with modified threads or fasteners with a separate non-metallic element or one fused to the threads. The former have fewer temperature and environmental limitations than the latter, but the latter do not encounter thread galling and other problems characteristic of the former.
It is an object of the present invention to provide an improved locking fastener assembly.
It is another object to provide a locking fastener assembly comprising only two components, a nut and a washer.
It is yet another object to provide a locking fastener assembly in which secure locking is achieved between a rotatable nut and a non-rotatable washer without the use of separate locking elements.
It is still another object to provide a locking fastener assembly including a new and improved locking mechanism.
It is a further object to provide a new and improved locking mechanism for a locking fastener assembly wherein a locking relationship is established directly between nut and washer.
It is yet a further object to provide a locking mechanism for a locking fastener assembly wherein a washer and nut interlock is established and a constant bearing load resiliently maintained when the assembly is employed to mount a vehicle wheel.
The foregoing and other objects of the invention are realized in a locking fastener assembly which comprises only a nut and a washer. Each is formed from medium carbon steel.
The washer includes a generally cylindrical washer body and a flange extending radially outward from the base of the body. A clamping surface is formed on the bottom of the flange and washer body base.
The top of the washer body has an annular, generally spherically concave load bearing surface formed on it. The load bearing surface includes an annularly extending series of inclined bearing faces forming a uniform undulation around the entire surface. A series of plateau surfaces between the inclined bearing faces form the upper peaks of the undulation. A series of valley surfaces between the inclined bearing faces form the valleys of the undulation. Each of the plateau and valley surfaces are spherically concave. Each of the inclined bearing faces is also spherically concave. The height of the plateau surface above the valley surface is slightly greater than the clearance between the threads in the nut and those on a vehicle axle spindle, for example, when the locking fastener assembly is in place.
The slightly concave washer body clamping surface on the bottom of the washer forms what approximates a shallow frustum of a cone. This surface is inclined upwardly from the outer periphery of the washer flange of its bottom toward the washer body axis.
The washer flange has a plurality of slots formed inwardly from its outer edge, at regular intervals around the flange. These slots permit intervening flange sections to resiliently flex, albeit only slightly, when the washer clamping surface is forced against an outer bearing race and is under the desired load.
An ear is formed inwardly of the base of the washer body, opposite the flange. The ear is designed to slide axially through a suitably formed slot in the threaded end section of an axle spindle to prevent the washer from rotating relative to the spindle as the nut is threaded onto this end section. In the alternative, a flat may be formed on the spindle and a corresponding flat formed inwardly of the washer body.
The nut includes a generally cylindrical nut body which is internally threaded. A hexagonal surface is formed around the periphery of the nut body to permit gripping the nut with a wrench.
Depending from the nut body is a unitarily formed annular skirt. The skirt is adapted to extend axially into the generally cylindrical body of the washer and then be formed outwardly under an undercut shoulder within the washer body to loosely, but securely, hold the washer and nut together.
The bottom of the nut body, above the skirt, has an annular, generally spherically convex load bearing surface formed on it. The load bearing surface includes an annularly extending series of inclined bearing faces forming a uniform undulation around the entire surface. A series of plateau surfaces between the inclined bearing faces form the lower peaks of the undulation. These plateau surfaces are spherically convex, with the same radius as the valley surfaces on the washer""s load bearing surface. Each of the inclined bearing faces is also spherically convex, with the same radius as the bearing faces on the washer""s nut bearing surface.
When the nut is threaded onto the axle spindle, the washer is pushed freely in front of it without rotating, until the slightly concave, frusto-conical clamping surfaces engage on the ends of the flange sections the inner bearing race of the outer bearing assembly supporting the wheel hub. Further axial travel of the washer is then resisted by the bearing race, first relatively lightly while the bearing races move closer together and then relatively firmly as the bearing races reach their operating positions.
Meanwhile, the peaks on the opposed undulating load bearing surfaces ride over each other with greater and greater difficulty as the load increases. Finally, they can slip past each other only when the flange sections on the washer begin to resiliently flex. The nut is then securely prevented from counter-rotating and loosening by the interlocking bearing faces and the resilient pressure of the washer.
In locked relationship, the spherically convex plateau surfaces in the load bearing surface of the nut seat flush against corresponding spherically concave valley surfaces in the load bearing surface of the washer. Also, the convex inclined leading bearing faces on the nut seat flush against the concave inclined trailing bearing faces of the washer and prevent the nut from backing off.